1. Field of the Invention
This invention relates to perfluoropolymer core/shell polymer.
2. Description of related Art
It has become desirable to provide melt-fabricable perfluoropolymer with higher fluidity at the melt-fabrication temperature so as to increase the production rate for the desired molded article, e.g. to increase extrusion rate for primary insulation or cable jacket for communications cable. The development of high fluidity perfluoropolymer has been accompanied by changes in perfluoropolymer composition such that the physical properties of the perfluoropolymer remain satisfactory. For convenience, melt fluidity is often referred to as Melt Flow Rate (MFR) which is in units of grams of polymer that will flow in 10 min from the Plastometer® of ASTM D 1238-94a under a specified load at a specified temperature established by the ASTM test for the particular perfluoropolymer involved. The higher the MFR, the higher is the fluidity of the perfluoropolymer. When fluidity is expressed in terms of melt viscosity, the higher the MFR, the lower is the melt viscosity. While the high MFR perfluoropolymer has enabled higher production rates to be achieved, the disadvantage has arisen that the high MFR perfluoropolymer is also more flowable (fluid) when exposed to high temperatures such as may be encountered in a fire in a building in which articles such as insulated/jacketed plenum cable are used. The result of this increased fluidity is that the perfluoropolymer melts and drips, the drips causing the creation of smoke, which is prohibited by the building code NFPA-255.
US2005/0187328 A1 discloses the addition of a substantial amount of inorganic char-forming agent together with a small amount of hydrocarbon polymer to counteract the deterioration of the physical properties that would be observed if the blend were only perfluoropolymer plus char-forming agent. While the resultant three-component blend is both non-flammable and non-smoking enough as plenum cable jacket to pass the NFPA-255 burn test, such jacket composition contains a substantial amount of non-perfluoropolymer, i.e. char-forming agent and hydrocarbon polymer, which can be a disadvantage in certain applications.
The problem is how to obtain a perfluoropolymer which possesses both a high melt flow rate, for ease of melt-fabrication, such as by extrusion or injection molding, and which also resists dripping (melt flow), when exposed to heat such as from a building fire.